The invention herein relates to alkali resistant glass articles. More particularly it relates to coatings to impart alkali resistance to glass fibers.
When glass fibers are used in alkaline environments, such as when they are used as fibrous reinforcement for Portland cement, they are rapidly attacked by the alkali and deteriorate rapidly. Since economic and environmental considerations have made the use of glass fiber for cement reinforcement much more attractive in recent years, there have been numerous efforts to render glass fiber less susceptible to alkaline attack. These efforts have had two principal directions: first, much effort has been directed toward developing glass compositions which are themselves resistant to alkaline attack. For instance, one type of glass composition which is commercially used and considered moderately alkaline resistant contains large amounts of zirconia. Fibers made of such compositions deteriorate much less rapidly in an alkaline environment than do fibers made of conventional glass compositions such as the well known "E glass." The alkali resistant glass compositions, however, are quite expensive and thus cannot be readily used for such purposes as cement reinforcement without unduly raising the cost of the finished cement product.
The second approach to imparting alkali resistance to glass articles has been to develop coatings for the glass fibers which will prevent the alkaline components from contacting and attacking the glass surface. Use of such coatings is intended to allow the glass fiber to be composed of inexpensive and conventional materials such as those in the aforementioned "E glass." Alternatively, use of such coatings on fibers of alkali resistant glass compositions would enhance that alkali resistance and significantly extend the useful life of the expensive alkali resistant fibers, thus improving the economics of their use for cement reinforcement and similar uses.
A number of possible coatings have been suggested in the prior art. Of these the coatings most pertinent to the present invention are those described in U.S. Pat. No. 4,013,478 issued to Meyer. Alkali resistance is imparted in the Meyer invention by coating the glass fibers with water soluble zinc salts of weak acids, particularly zinc acetate, zinc formate, or zinc oxalate. Such coatings provide only limited alkali resistance to glass fibers, particularly under more severe conditons, and because of their water solubility can be detrimentally affected by the water present in Portland cement during the cement curing process.
It is therefore an object of this invention to provide a coating for glass fiber which will impart a significant degree of alkali resistance to the glass fiber, and which can be readily applied, and which is retained on the glass fiber in an alkaline, especially cement, environment. It is also an object of the invention to provide an alkali resistant coated glass fiber article.